The invention relates to an inner torch for the electric-arc spraying of cavities, in particular of cylinder contact surfaces, as is known, for example, from the generically determinative German Patent DE 198 41 617 A1 which discloses an inner torch for the electric-arc spraying of cavities, in particular of cylinder contact surfaces. The inner torch has two torch tubes which are provided with heating electrodes made of wire. The electrodes are melted in an electric arc. The inner torch also has a gas feed for a process gas which is provided for transporting and spraying the molten wire material in the direction of the cavity surface to be coated. The (electrodes) wires are guided towards one another, by way of the torch tubes, at the outlet and in the region of the electric arc. The electric arc in the contact region of the wires, is arranged in the region of the flow of the discharged process gas. The flow of the discharged process gas, referred to as the main gas flow direction for the sake of simplicity hereinbelow, is arranged transversely to the main transporting direction on the wires, this direction being defined by the torch tubes. Layers which are sprayed by such an inner torch onto, in particular, a metallic substrate, preferably a cylinder contact surface, have, inter alia, a high porosity and/or pores with an unacceptable large average pore diameter.
The object of the invention is further to develop the previously known inner torch to the effect that it gives rise to sprayed layers which have a lower porosity and/or pores with a smaller average pore diameter.
The object is achieved according to the invention by an inner torch wherein the wire is bent at least twice so that the contact point of the two wires, and thus the electric arc itself, has high positional stability in the event of fluctuations in current and/or voltage. It is this positional stability which results in the layers which are sprayed by the inner torch according to the invention having a negligible porosity. Furthermore, it is also the case with these layers that the average pore diameter is smaller than in the case of the prior art.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.